Monday, September 5, 2011

If you were ever a kid - as I was a couple centuries ago - then you know how
irresistible a mysterious glob of spittle can be.

A golf ball-sized lump of
white froth, found clinging to a plant stem in the local weed patch, is a captivating kid-magnet
that simply must be investigated. We didn't have the internet or computers
back then, and they didn't even invent guidebooks until we were much older. So for years I didn't know
if the spittle was made by the plant or by the little bug that we sometimes
found hiding in the foam.

Times have changed all of us kids, but the captivating "spittlebugs" remain.

Today we know that
spittlebugs (family Cercopidae) are named for the white froth made by the larval stages of
this very common insect. We also know the adults as "froghoppers," and as the high jump champions of the
insect world, thank you very much. Move over fleas.

But first, about that froth.

Spittlebugs overwinter as egg masses that hatch in early summer. The wingless larvae,
about one-quarter inch in size, create the frothy white abodes where they
will grow through five moults before leaving home in late summer as adults. As
larvae, they feed on plant sap sucked out through a specialized, needle-like
feeding tube.

Sugar-rich phloem sap moves down from the plant's photosynthetic
leaves, but for some reason the spittlebugs tap into the sugar-poor but
mineral-laden xylem sap flowing up from the water-pumping roots. The larvae
have to drink lots of liquid to grow into an adult, and therefore they also
have to excrete lots of liquid.

So the so-called "spittle" is really a gentlemanly way of saying piddle. It
really originates from the other end of the bug. But wait, it gets even better. The larvae also use the tip of their abdomen to, um, "blow
bubbles" into this liquid to form froth. What possible body function combination could be more kid-captivating?

The sticky froth serves the spittlebug well. It hides the bug, protects it from
parasites, and prevents it from drying out. It also deters some predators (and
attracts some boys) with the "yuck factor."

1/4" long spittlebugs require five instars, or larval stages, before turning into adults and leaving the spittle behind.

In one experiment, predacious ants tended to leave the larval bugs alone even after the bugs were
removed from their spittle. After touching the bugs or spittle, the ants
immediately began grooming their antennae. But when the investigators (three
grown-up boys at the University of Wisconsin) rinsed the spittle off, the ants
carried most (67%) of the bugs home for dinner.

The ants, meanwhile, are one of our most underestimated critters. While the spittlebugs'
froth apparently irritates their appendages, the ants have nonetheless learned
how to use the sticky froth to build their own temporary housing.
Up in some of the same plant neighborhoods where spittlebugs live, ground-dwelling
ants also tend to their herds of aphids - yet another fascinating,
plant-juice-sucking insect (more on aphids in a later edition).

Ants defend
aphids from predators while drinking the sugar-rich "honeydew"
excreted from the aphids' rear ends. Up in the plants, the ground-dwelling ants
sometimes build temporary tents out of soil and thatch to corral and protect
their aphid herds. What do they use to glue their aphid-tents together with?

But the ants don't like to touch spittle, so they carry up pieces of dry soil and stick
them to the outside of the spittle mass. The spittle gets soaked up by the soil
and thatch and, presto, the ants have a tent to camp in and use to protect
their herds. Sometimes, this also enables the ants to capture and consume
the larval spittlebug.

Ant predation has localized effects on spittlebug populations, but many spittlebugs still piddle their way through youth to become high-jump-champion adults.
When spittlebugs reach this golden age, about one month old, we call them
"froghoppers."

Three froghoppers on a knapweed bud

Froghoppers (adult spittlebugs) are golden-brown insects less than one-half inch long.
They don't use their wings very often, and they never make spittle for
protection from predators. When threatened, froghoppers simply leap away. They
also use this Olympian talent to move from plant to plant.

Froghopper jumps have been measured at just over 27 inches high, a little higher than the
best flea athlete. But froghoppers weigh in at more than 60 times heavier than
fleas. If you compare how much force animals can generate per body weight,
froghoppers win hands-down: froghoppers 400X, fleas 135X, humans 2-3X.

During a froghopper jump, the initial acceleration is somewhere in the neighborhood of
8,900 mph. A human astronaut blasting off into space experiences a g-force of 5
gravities or less. Our neighborhood froghopper, on the other hand, generates a
g-force of more than 400 gravities on a good jump.

That's substantially more than a little bit impressive.

For a neighborhood bug that lives in a patch of weeds, grows up in spittle, and
weighs less than 0.000026 of a pound, the froghoppers posses athletic skills
that can impress and inspire kids of any age. If only we lived in a just world, we would see
school mascots named, "The Spittlebugs," and professional sports
teams named, "The Froghoppers."
If only.